Monitoring the in-vitro extracellular matrix remodeling of tissue engineered vascular grafts Hannah Schmidta, Jonathan Vande Geesta, b, c Department of Bioengineering, bMcGowan Institute for Regenerative Medicine, cVascular Medicine Institute a
Hannah Schmidt is a fourth-year undergraduate studying Bioengineering at the University of Pittsburgh. She conducted research on tissue engineered vascular grafts with Dr. Vande Geest’s lab for two years and, in the future, plans to attend medical school. Hannah Schmidt
Dr. Jonathan Vande Geest is a Professor in the Department of Bioengineering, Department of Mechanical Engineering and Material Science, the Department of Ophthalmology, the McGowan Institute for Regenerative Medicine, the Louis J. Fox Center for Vision Restoration, and Dr. Jonathan Vande the Vascular Medicine Institute at the Geest University of Pittsburgh. He received his BS in Biomedical Engineering from the University of Iowa in 2000 and his PhD in Bioengineering from the University of Pittsburgh in 2005. Dr. Vande Geest began his career at the University of Arizona in the Department of Aerospace and Mechanical Engineering and joined the U of A’s Department of Biomedical Engineering in 2009. Dr. Vande Geest returned to the University of Pittsburgh in January of 2016.
Significance Statement
It can be difficult to visualize longitudinal structural changes in-vivo in biological systems, oftentimes due to the necessity of destructive imaging. This research successfully overcomes this challenge for the study of vascular graft collagen remodeling by developing two-photon imaging parameters which can be generalized to broad in-vivo tissue engineering applications.
Category: Methods
Keywords: tissue engineered vascular graft, collagen remodeling, two-photon microscopy
92 Undergraduate Research at the Swanson School of Engineering
Abstract
Heart disease is the leading cause of death in the United States for both men and women. Coronary artery bypass grafts (CABG) are frequently implanted to restore blood flow to the heart, but these small diameter vascular grafts frequently accumulate clots and become narrow, making them ineffective. The Soft Tissue Biomechanics Laboratory (STBL) is seeking to create a tissue engineered vascular graft (TEVG) to address these issues of compliance mismatch and thrombosis in small diameter grafts. It is particularly important to assess the extracellular matrix remodeling (ECM) capabilities of our TEVGs in order to monitor the in-vivo transition of TEVGs from synthetic graft to host remodeled tissue. This study therefore aims to develop an in-vitro imaging method for quantifying ECM remodeling of TEVGs. We were able to determine optimal imaging parameters and show that two-photon imaging can be used to characterize structural changes of collagen in the ECM, which will be used in the future to evaluate TEVG efficacy.
1. Introduction
Heart disease was responsible for 633,842 deaths in 2015 [1], making it the leading cause of death in the United States for both men and women. Coronary artery disease (CAD) in particular is responsible for nearly half of all heart disease cases [2]. Coronary artery bypass grafting (CABG) from autologous vessels is a common treatment used to restore blood flow to the heart in patients with CAD, but suffers from high rates of thrombosis and restenosis, with reintervention rates reported to be as high as 8.8% [3]. Providing a functional tissue engineered vascular graft (TEVG) for CABG surgeries would therefore result in substantial improvements in patient care. The Soft Tissue Biomechanics Laboratory is creating a TEVG for small diameter CABG applications to address these issues. Our team aims to create a primarily acellular, biocompatible, and compliance matched graft. This study will focus on evaluation of the overall function of the TEVGs. Because the grafts are primarily acellular when implanted, we must ensure that native cells can migrate and proliferate within the graft to transition TEVGs into living tissue. This transition is accomplished primarily through the production of a collagen extracellular matrix (ECM) by vascular smooth muscle cells as the TEVG degrades. It is therefore necessary to quantify the in-vitro ECM remodeling of TEVGs to understand the graft’s in-vivo transition from polymer-based scaffold to host remodeled tissue. Current approaches to imaging ECM remodeling include the work of Hjortnaes et al. 2009 [4], which showed that TEVG remodeling in-vivo can be monitored using laser scanning fluorescence imaging. The study relied on injection of nondestructive imaging agents which provided signal in response to proteolytic activity. Though they were successfully able to see changes in the enzymatic activity of TEVGs in a mouse model, graft degradation and new ECM formation cannot be directly measured using this method because it does not actually visualize the collagen or the TEVG itself. Rather, it uses enzymatic activity to make inferences about ECM remodeling. A different method is required to visualize degradation and collagen formation first-hand.
